U.S. patent number 11,319,487 [Application Number 15/976,197] was granted by the patent office on 2022-05-03 for semiconductor nanocrystal particles and devices including the same.
This patent grant is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. The grantee listed for this patent is SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Eun Joo Jang, Hyun A Kang, Tae Hyung Kim, Jeong Hee Lee.
United States Patent |
11,319,487 |
Lee , et al. |
May 3, 2022 |
Semiconductor nanocrystal particles and devices including the
same
Abstract
A semiconductor nanocrystal particle including zinc (Zn),
tellurium (Te) and selenium (Se), a method of producing the same,
and an electronic device including the same are disclosed. In the
semiconductor nanocrystal particle, an amount of the tellurium is
less than an amount of the selenium, the particle includes a core
including a first semiconductor material including zinc, tellurium,
and selenium and a shell disposed on at least a portion of the core
and including a second semiconductor material having a different
composition from the first semiconductor material, and the
semiconductor nanocrystal particle emits blue light including a
maximum peak emission at a wavelength of less than or equal to
about 470 nanometers.
Inventors: |
Lee; Jeong Hee (Seongnam-si,
KR), Jang; Eun Joo (Suwon-si, KR), Kang;
Hyun A (Suwon-si, KR), Kim; Tae Hyung (Seoul,
KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
SAMSUNG ELECTRONICS CO., LTD. |
Suwon-si |
N/A |
KR |
|
|
Assignee: |
SAMSUNG ELECTRONICS CO., LTD.
(Gyeonggi-Do, KR)
|
Family
ID: |
1000006281092 |
Appl.
No.: |
15/976,197 |
Filed: |
May 10, 2018 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20180327665 A1 |
Nov 15, 2018 |
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Foreign Application Priority Data
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May 11, 2017 [KR] |
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10-2017-0058474 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K
11/02 (20130101); C09K 11/883 (20130101); C09K
11/565 (20130101); B82Y 20/00 (20130101); Y10S
977/824 (20130101); H01L 51/502 (20130101); Y10S
977/95 (20130101); Y10S 977/892 (20130101); B82Y
40/00 (20130101); Y10S 977/774 (20130101) |
Current International
Class: |
C09K
11/88 (20060101); C09K 11/56 (20060101); C09K
11/02 (20060101); B82Y 20/00 (20110101); H01L
51/50 (20060101); B82Y 40/00 (20110101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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101525524 |
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May 2015 |
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KR |
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2005001889 |
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Jan 2005 |
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WO |
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2008063652 |
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May 2008 |
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WO |
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Other References
Sonawane. A case study: Te in ZnSe and Mn-doped ZnSe quantum dots.
Nanotechnology 22 (2011) 305702 (7pp) (Year: 2011). cited by
examiner .
Chunliang Li et al., "Synthesis of Cd-free water-soluble
ZnSe(1-x)Te(x) nanocrystals with high luminescence in the blue
region", Journal of Colloid and Interface Science, Feb. 14, 2008,
pp. 468-476, vol. 321, ScienceDirect. cited by applicant .
Extended European Search Report dated Oct. 2, 2018, of the
corresponding European Patent Application No. 18171712.5. cited by
applicant.
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Primary Examiner: Hoban; Matthew E.
Attorney, Agent or Firm: Cantor Colburn LLP
Claims
What is claimed is:
1. A semiconductor nanocrystal particle comprising zinc, tellurium,
and selenium, wherein an amount of the tellurium is less than an
amount of the selenium and a mole ratio of the tellurium to the
selenium is less than 0.01:1, the particle comprises a core
comprising a first semiconductor material comprising zinc,
tellurium, and selenium and a shell disposed on at least a portion
of the core and comprising a second semiconductor material having a
different composition from the first semiconductor material, the
semiconductor nanocrystal particle emits blue light comprising a
maximum peak emission at a wavelength of greater than or equal to
449 nanometers (nm) and less than or equal to about 470 nanometers
(nm), and wherein the maximum peak emission has a full width at
half maximum of less than or equal to about 34 nm.
2. The semiconductor nanocrystal particle of claim 1, wherein a
mole ratio of the tellurium to the selenium is greater than or
equal to about 0.001:1.
3. The semiconductor nanocrystal particle of claim 1, wherein a
mole ratio of the tellurium to the selenium is from about 0.001:1
to about 0.007:1.
4. The semiconductor nanocrystal particle of claim 1, wherein an
amount of the zinc is greater than an amount of the selenium.
5. The semiconductor nanocrystal particle of claim 4, wherein a
mole ratio of the tellurium to the zinc is less than or equal to
about 0.03:1.
6. The semiconductor nanocrystal particle of claim 1, wherein an
amount of the tellurium is less than or equal to about 1 weight
percent, based on a total weight of the semiconductor nanocrystal
particle.
7. The semiconductor nanocrystal particle of claim 1, wherein a
size of the core is greater than or equal to about 2
nanometers.
8. The semiconductor nanocrystal particle of claim 1, wherein the
shell comprises a plurality of layers and adjacent layers of the
plurality of layers comprise different semiconductor materials.
9. The semiconductor nanocrystal particle of claim 8, wherein the
shell comprises a first layer disposed directly on the core, and an
outermost layer, wherein the first layer comprises ZnSeS and the
outermost layer comprises ZnS.
10. The semiconductor nanocrystal particle of claim 1, wherein the
maximum peak emission is at a wavelength of greater than or equal
to 450 nanometers to about 470 nanometers.
11. The semiconductor nanocrystal particle of claim 1, wherein the
maximum peak emission has a full width at half maximum of less than
or equal to about 30 nanometers.
12. The semiconductor nanocrystal particle of claim 1, wherein the
semiconductor nanocrystal particle has quantum efficiency of
greater than or equal to about 60%.
13. The semiconductor nanocrystal particle of claim 1, wherein the
semiconductor nanocrystal particle does not comprise cadmium.
14. The semiconductor nanocrystal particle of claim 1, wherein the
semiconductor nanocrystal particle has a multipod shape.
15. A method of producing the semiconductor nanocrystal particle of
claim 1, comprising preparing a zinc precursor solution comprising
a zinc precursor and an organic ligand; heating the zinc precursor
solution at a first reaction temperature and adding a selenium
precursor and a tellurium precursor, and optionally an organic
ligand, to form a first semiconductor nanocrystal core comprising
zinc, selenium, and tellurium; preparing a first shell precursor
solution comprising a metal-containing first shell precursor and an
organic ligand; and heating the first shell precursor solution at a
second reaction temperature and adding the first semiconductor
nanocrystal core and a second shell precursor to form a shell of a
second semiconductor nanocrystal on the first semiconductor
nanocrystal core, the second shell precursor comprising a non-metal
element.
16. The method of claim 15, wherein the zinc precursor comprises a
Zn powder, ZnO, an alkylated Zn compound, a Zn alkoxide, a Zn
carboxylate, a Zn nitrate, a Zn perchlorate, a Zn sulfate, a Zn
acetylacetonate, a Zn halide, a Zn cyanide, a Zn hydroxide, or a
combination thereof, the selenium precursor comprises
selenium-trioctylphosphine, selenium-tributylphosphine,
selenium-triphenylphosphine, selenium-diphenylphosphine, or a
combination thereof, and the tellurium precursor comprises
tellurium-tributylphosphine, tellurium-triphenylphosphine,
tellurium-diphenylphosphine, or a combination thereof.
17. The method of claim 15, wherein an amount of the selenium
precursor is greater than or equal to about 20 moles and less than
or equal to about 60 moles, based on one mole of the tellurium
precursor.
18. The method of claim 15, wherein the first shell precursor
comprises zinc and the second shell precursor comprises selenium,
sulfur, or a combination thereof.
19. The method of claim 15, wherein the organic ligand comprises
RCOOH, RNH.sub.2, R.sub.2NH, R.sub.3N, RSH, RH.sub.2PO, R.sub.2HPO,
R.sub.3PO, RH.sub.2P, R.sub.2HP, R.sub.3P, ROH, RCOOR,
RPO(OH).sub.2, R.sub.2POOH, RHPOOH, or a combination thereof
(wherein, R is the same or different and is independently a C1 to
C24 substituted or unsubstituted aliphatic hydrocarbon group, a C6
to C20 substituted or unsubstituted aromatic hydrocarbon group, or
a combination).
20. An electronic device comprising the semiconductor nanocrystal
particle of claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to Korean Patent Application No.
10-2017-0058474 filed in the Korean Intellectual Property Office on
May 11, 2017, and all the benefits accruing therefrom under 35
U.S.C. .sctn. 119, the entire contents of which are incorporated
herein by reference.
BACKGROUND
1. Field
A semiconductor nanocrystal particle and a device including the
same are disclosed.
2. Description of the Related Art
Unlike bulk materials, intrinsic physical characteristics (e.g.,
energy bandgaps and melting points) of nanoparticles may be
controlled by changing the nanoparticle sizes. For example, a
semiconductor nanocrystal particle (also known as a quantum dot) is
a crystalline material having a size of several nanometers. The
semiconductor nanocrystal particle has such a small size that it
has a large surface area per unit volume and exhibits a quantum
confinement effect, and thus may have different properties than
bulk materials having the same composition. A quantum dot may
absorb light from an excitation source to be excited, and may emit
energy corresponding to its energy bandgap.
Quantum dots may be synthesized using a vapor deposition method
such as metal organic chemical vapor deposition (MOCVD), molecular
beam epitaxy (MBE), or the like, a wet chemical method including
adding precursor materials to an organic solvent to grow crystals,
or the like. In the wet chemical method, organic compounds such as
ligands/coordinating solvents may be coordinated on, e.g., bound
to, surfaces of nanocrystals to control a crystal growth during the
crystal growth.
SUMMARY
An embodiment provides a cadmium-free semiconductor nanocrystal
particle capable of emitting blue light with improved
efficiency.
An embodiment provides a method of manufacturing the semiconductor
nanocrystal particle.
An embodiment provides an electronic device including the
semiconductor nanocrystal particle.
In an embodiment, a semiconductor nanocrystal particle includes
zinc (Zn), tellurium (Te) and selenium (Se),
wherein an amount of the tellurium is less than an amount of the
selenium (wherein if the amount of Te is a and the amount of Se is
b, a<b),
the particle includes a core including a first semiconductor
material including zinc, tellurium, and selenium and a shell
disposed on at least a portion of the core and including a second
semiconductor material having a different composition from the
first semiconductor material, and
the semiconductor nanocrystal particle emits blue light including a
maximum peak emission at a wavelength of less than or equal to
about 470 nanometers (nm).
The semiconductor nanocrystal particle may have a mole ratio of the
tellurium to the selenium of less than or equal to about 0.05:1
(for example, as measured by an inductively coupled plasma-atomic
emission spectroscopy (ICP-AES)).
In the semiconductor nanocrystal particle, for example, the mole
ratio of the tellurium to the selenium may be less than about
0.024:1.
In the semiconductor nanocrystal particle, an amount of the zinc
may be greater than an amount of the selenium.
The semiconductor nanocrystal particle may have a mole ratio of the
tellurium to the zinc of less than or equal to about 0.03:1 (for
example, as measured by an inductively coupled plasma-atomic
emission spectroscopy).
The semiconductor nanocrystal particle may include the tellurium in
an amount of about 1 weight percent (wt %) or less, based on a
total weight thereof.
The first semiconductor material may include ZnTe.sub.xSe.sub.1-x
(wherein, x is greater than about 0 and less than or equal to about
0.05).
A size of the core may be greater than or equal to about 2 nm.
A size of the core may be less than or equal to about 6 nm.
The second semiconductor material may include zinc, selenium, and
sulfur.
The shell may include a plurality of layers and adjacent layers of
the plurality of the layers may include semiconductor materials
different from each other.
The shell may include a first layer disposed directly on the core
and an outermost layer, wherein the first layer may include ZnSeS
and the outermost layer may include ZnS.
The semiconductor nanocrystal particle may emit blue light having
maximum peak emission that may be at a wavelength of about 430 nm
to about 470 nm.
The maximum peak emission may have a full width at half maximum
(FWHM) of less than or equal to about 50 nm.
The semiconductor nanocrystal particle may have quantum efficiency
of greater than or equal to about 60%.
The semiconductor nanocrystal particle may have a size of greater
than or equal to about 3 nm.
The semiconductor nanocrystal particle may have a size of less than
or equal to about 50 nm.
The semiconductor nanocrystal particle may not include cadmium.
The semiconductor nanocrystal particle may have a multi-pod
shape.
In an embodiment, a method of producing the semiconductor
nanocrystal particle includes
preparing a zinc precursor solution including a zinc precursor and
an organic ligand;
heating the zinc precursor solution at a first reaction temperature
and adding a selenium precursor and a tellurium precursor, and
optionally together with an organic ligand, thereto to form a first
semiconductor nanocrystal core including zinc, selenium, and
tellurium;
preparing a first shell precursor solution including a
metal-containing first shell precursor and an organic ligand;
and
heating the first shell precursor solution at a second reaction
temperature and adding the first semiconductor nanocrystal core and
a second shell precursor thereto to form a shell of a second
semiconductor nanocrystal on the first semiconductor nanocrystal
core, the second shell precursor comprising a non-metal
element.
The method may include separating the first semiconductor
nanocrystal core and dispersing it in an organic solvent to prepare
a core solution.
The zinc precursor may include a Zn powder, an alkylated Zn
compound, a Zn alkoxide, a Zn carboxylate, a Zn nitrate, a Zn
perchlorate, a Zn sulfate, a Zn acetylacetonate, a Zn halide, a Zn
cyanide, a Zn hydroxide, or a combination thereof.
The selenium precursor may include selenium-trioctylphosphine
(Se-TOP), selenium-tributylphosphine (Se-TBP),
selenium-triphenylphosphine (Se-TPP), selenium-diphenylphosphine
(Se-DPP), or a combination thereof.
The tellurium precursor may include tellurium-trioctylphosphine
(Te-TOP), tellurium-tributylphosphine (Te-TBP),
tellurium-triphenylphosphine (Te-TPP), or a combination
thereof.
An amount of the selenium precursor may be greater than or equal to
about 20 moles (mols), based on one mole of the tellurium
precursor.
An amount of the selenium precursor may be less than or equal to
about 60 mols, based on one mole of the tellurium precursor.
The first shell precursor may include zinc, and the second shell
precursor may include selenium, sulfur, or a combination
thereof.
The organic ligand may include RCOOH, RNH.sub.2, R.sub.2NH,
R.sub.3N, RSH, RH.sub.2PO, R.sub.2HPO, R.sub.3PO, RH.sub.2P,
R.sub.2HP, R.sub.3P, ROH, RCOOR, RPO(OH).sub.2, RHPOOH, R.sub.2POOH
(wherein, R is the same or different and independently is a C1 to
C24 substituted or unsubstituted aliphatic hydrocarbon group, a C6
to C20 substituted or unsubstituted aromatic hydrocarbon group, or
a combination thereof), or a combination thereof.
In an embodiment, an electronic device includes the aforementioned
semiconductor nanocrystal particle.
The electronic device may be a display device, a light emitting
diode (LED), a quantum dot light emitting diode (QLED), an organic
light emitting diode (OLED), a sensor, an image sensor, or a solar
cell electronic device.
A cadmium-free semiconductor nanocrystal particle capable of
emitting blue light may be provided. The semiconductor nanocrystal
particle may be applied to various display devices, biolabeling
(biosensor, bioimaging), a photodetector, a solar cell, a hybrid
composite, or the like.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other advantages and features of this disclosure will
become more apparent by describing in further detail exemplary
embodiments thereof with reference to the accompanying drawings, in
which:
FIG. 1 is a schematic cross-sectional view of a semiconductor
nanocrystal according to a non-limiting embodiment.
FIG. 2 is a schematic cross-sectional view of a quantum dot (QD)
LED device according to a non-limiting embodiment.
FIG. 3 is a schematic cross-sectional view of a QD LED device
according to a non-limiting embodiment.
FIG. 4 is a schematic cross-sectional view of a QD LED device
according to a non-limiting embodiment.
FIG. 5 shows ultraviolet-visible (UV-Vis) absorption spectra of the
ZnTeSe cores produced in Examples.
FIG. 6 shows photoluminescence (PL) spectra of the ZnTeSe cores
produced in Examples.
FIG. 7 shows a transmission electron microscope (TEM) image of the
ZnTeSe cores produced in Examples.
FIG. 8 shows a High-Resolution Transmission Electron Microscopy
(HRTEM) image of the ZnTeSe cores produced in Examples.
FIG. 9 shows an X-ray diffraction spectrum of the ZnTeSe core
produced in Example.
FIG. 10 shows UV-vis absorption spectrums of the semiconductor
nanocrystals during a production (core, A step, B step, and
produced core-shell) in Example 3, respectively.
FIG. 11 shows PL spectrums of the semiconductor nanocrystals during
production (core, A step, B step, and produced core-shell) in
Example 3, respectively.
FIG. 12 shows a transmission electron microscope image of the
semiconductor nanocrystals produced in Example 3.
FIG. 13 shows a transmission electron microscopy-energy dispersive
X-ray (TEM-EDX) (elemental mapping) analysis result of the
semiconductor nanocrystal produced in Example 3.
DETAILED DESCRIPTION
Advantages and characteristics of this disclosure, and a method for
achieving the same, will become evident referring to the following
example embodiments together with the drawings attached hereto.
However, the embodiments should not be construed as being limited
to the embodiments set forth herein. Unless otherwise defined, all
terms used in the specification (including technical and scientific
terms) may be used with meanings commonly understood by a person
having ordinary knowledge in the art. The terms defined in a
generally-used dictionary may not be interpreted ideally or
exaggeratedly unless clearly defined. In addition, unless
explicitly described to the contrary, the word "comprise" and
variations such as "comprises" or "comprising", will be understood
to imply the inclusion of stated elements but not the exclusion of
any other elements.
Further, the singular includes the plural unless mentioned
otherwise.
In the drawings, the thickness of layers, films, panels, regions,
etc., are exaggerated for clarity. Like reference numerals
designate like elements throughout the specification.
It will be understood that when an element such as a layer, film,
region, or substrate is referred to as being "on" another element,
it can be directly on the other element or intervening elements may
also be present. In contrast, when an element is referred to as
being "directly on" another element, there are no intervening
elements present.
It will be understood that, although the terms "first," "second,"
"third" etc. may be used herein to describe various elements,
components, regions, layers and/or sections, these elements,
components, regions, layers and/or sections should not be limited
by these terms. These terms are only used to distinguish one
element, component, region, layer or section from another element,
component, region, layer or section. Thus, "a first element,"
"component," "region," "layer" or "section" discussed below could
be termed a second element, component, region, layer or section
without departing from the teachings herein.
The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting. As
used herein, the singular forms "a," "an," and "the" are intended
to include the plural forms, including "at least one," unless the
content clearly indicates otherwise. "At least one" is not to be
construed as being limited to "a" or "an." "Or" means "and/or." As
used herein, the term "and/or" includes any and all combinations of
one or more of the associated listed items. It will be further
understood that the terms "comprises" and/or "comprising," or
"includes" and/or "including" when used in this specification,
specify the presence of stated features, regions, integers, steps,
operations, elements, and/or components, but do not preclude the
presence or addition of one or more other features, regions,
integers, steps, operations, elements, components, and/or groups
thereof.
"About" or "approximately" as used herein is inclusive of the
stated value and means within an acceptable range of deviation for
the particular value as determined by one of ordinary skill in the
art, considering the measurement in question and the error
associated with measurement of the particular quantity (i.e., the
limitations of the measurement system). For example, "about" can
mean within one or more standard deviations, or within .+-.30%,
20%, 10%, or 5% of the stated value.
Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
disclosure belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and the present
disclosure, and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
Exemplary embodiments are described herein with reference to cross
section illustrations that are schematic illustrations of idealized
embodiments. As such, variations from the shapes of the
illustrations as a result, for example, of manufacturing techniques
and/or tolerances, are to be expected. Thus, embodiments described
herein should not be construed as limited to the particular shapes
of regions as illustrated herein but are to include deviations in
shapes that result, for example, from manufacturing. For example, a
region illustrated or described as flat may, typically, have rough
and/or nonlinear features. Moreover, sharp angles that are
illustrated may be rounded. Thus, the regions illustrated in the
figures are schematic in nature and their shapes are not intended
to illustrate the precise shape of a region and are not intended to
limit the scope of the present claims.
As used herein, when a definition is not otherwise provided,
"substituted" refers to a compound or a moiety wherein at least one
of hydrogen atoms thereof is replaced by a substituent, wherein the
substituent may be a C1 to C30 alkyl group, a C2 to C30 alkenyl
group, a C2 to C30 alkynyl group, a C6 to C30 aryl group, a C7 to
C30 alkylaryl group, a C1 to C30 alkoxy group, a C1 to C30
heteroalkyl group, a C3 to C30 heteroalkylaryl group, a C3 to C30
cycloalkyl group, a C3 to C15 cycloalkenyl group, a C6 to C30
cycloalkynyl group, a C2 to C30 heterocycloalkyl group, a halogen
(--F, --Cl, --Br, or --I), a hydroxy group (--OH), a nitro group
(--NO.sub.2), a cyano group (--CN), an amino group (--NRR' wherein
R and R' are independently hydrogen or a C1 to C6 alkyl group), an
azido group (--N.sub.3), an amidino group (--C(.dbd.NH)NH.sub.2)),
a hydrazino group (--NHNH.sub.2), a hydrazono group
(.dbd.N(NH.sub.2)), an aldehyde group (--C(.dbd.O)H), a carbamoyl
group (--C(O)NH.sub.2), a thiol group (--SH), an ester group
(--C(.dbd.O)OR, wherein R is a C1 to C6 alkyl group or a C6 to C12
aryl group), a carboxyl group (--COOH) or a salt thereof
(--C(.dbd.O)OM, wherein M is an organic or inorganic cation), a
sulfonic acid group (--SO.sub.3H) or a salt thereof (--SO.sub.3M,
wherein M is an organic or inorganic cation), a phosphoric acid
group (--PO.sub.3H.sub.2) or a salt thereof (--PO.sub.3MH or
--PO.sub.3M.sub.2, wherein M is an organic or inorganic cation), or
a combination thereof.
As used herein, "aliphatic" refers to a saturated or unsaturated
linear or branched hydrocarbon group. An aliphatic group may be an
alkyl, alkenyl, or alkynyl group, for example.
As used herein, "aromatic" means an organic compound or group
comprising at least one unsaturated cyclic group having delocalized
pi electrons. The term encompasses both hydrocarbon aromatic
compounds and heteroaromatic compounds.
As used herein, a hydrocarbon group refers to a group including
carbon and hydrogen (e.g., an alkyl, alkenyl, alkynyl, or aryl
group). The hydrocarbon group may be a group having a monovalence
or greater formed by removal of one or more hydrogen atoms from,
alkane, alkene, alkyne, or arene. In the hydrocarbon group, at
least one methylene may be replaced by an oxide moiety, a carbonyl
moiety, an ester moiety, --NH--, or a combination thereof. As used
herein, "alkyl" refers to a linear or branched saturated monovalent
hydrocarbon group (methyl, ethyl hexyl, etc.).
As used herein, "alkenyl" refers to a linear or branched monovalent
hydrocarbon group having one or more carbon-carbon double bond.
As used herein, "alkynyl" refers to a linear or branched monovalent
hydrocarbon group having one or more carbon-carbon triple bond.
As used herein, "aryl" refers to a group formed by removal of at
least one hydrogen from an aromatic group (e.g., a phenyl or
naphthyl group).
As used herein, "hetero" refers to one including one or more (e.g.,
1 to 3) heteroatom of N, O, S, Si, P, or a combination thereof.
As used herein, "Group" refers to a group of Periodic Table.
A core-shell structure may improve photoluminescence properties of
quantum dots, but most of conventional core-shell quantum dots
having desirable properties may include cadmium. Provided herein
are cadmium-free semiconductor nanocrystal particles having
desirable photoluminescence properties.
Semiconductor nanocrystal particles (hereinafter, also referred to
as a quantum dot) may absorb light from an excitation source and
may emit light corresponding to an energy bandgap thereof. The
energy bandgap of the quantum dot may be changed depending on a
size and a composition thereof. For example, as the size of the
quantum dot increases, the quantum dot may have a narrower energy
bandgap and may show an increased light emitting wavelength.
Semiconductor nanocrystals have drawn attention as a light emitting
material in various fields such as a display device, an energy
device, or a bio light emitting device.
Quantum dots having photoluminescence properties may include
cadmium (Cd). The cadmium may raise severe environmental and/or
health issues and is a restricted element defined under Restriction
of Hazardous Substances Directive (RoHS) in a plurality of
countries. Accordingly, there remain needs for development of a
cadmium-free quantum dot having improved photoluminescence
characteristics. In order to be applied to a QLED display device, a
quantum dot having a relatively narrow full width at half maximum
(FWHM) and capable of emitting light of pure blue (e.g., PL peak
around 455 nm) is desired. For example, a blue light emitting
material is required for a display device having a relatively high
(e.g., about 90% or greater) color reproducibility under a next
generation color standard such as BT2020. A cadmium-free quantum
dot having desirable photoluminescence properties and PL peak
within the foregoing ranges is provided.
A semiconductor nanocrystal particle according to an embodiment has
a structure and a composition that will be described herein, and
thereby may not include cadmium while emitting blue light.
The semiconductor nanocrystal particle includes zinc (Zn),
tellurium (Te) and selenium (Se). In the semiconductor nanocrystal
particle, an amount of the tellurium is less than that of the
selenium. The particle may have a core-shell structure having a
core including a first semiconductor material including zinc,
tellurium, and selenium and a shell that is disposed on at least a
portion of the core and includes a second semiconductor material
having a different composition from the first semiconductor
material (see FIG. 1). The semiconductor nanocrystal particle emits
blue light having a maximum peak emission at a wavelength of less
than or equal to about 470 nm. The first semiconductor material of
the core may include a ZnSe material including a small amount of
tellurium (Te). The core may have a cubic (zinc blend) crystal
structure. The core may include ZnTe.sub.xSe.sub.1-x (wherein, x is
greater than about 0 and less than or equal to about 0.05). The
wavelength of the maximum light emitting peak of the semiconductor
nanocrystal particle may be increased by increasing a ratio of an
amount of tellurium relative to an amount of selenium in the core.
In the core, the amount of the tellurium may be greater than or
equal to about 0.001 moles, greater than or equal to about 0.005
moles, greater than or equal to about 0.006 moles, greater than or
equal to about 0.007 moles, greater than or equal to about 0.008
moles, greater than or equal to about 0.009 moles, greater than or
equal to about 0.01 moles, or greater than or equal to about 0.02
moles based on one mole of the selenium. In the core, the amount of
the tellurium may be less than or equal to about 0.053 moles, for
example, less than or equal to about 0.05 moles, less than or equal
to about 0.049 moles, less than or equal to about 0.048 moles, less
than or equal to about 0.047 moles, less than or equal to about
0.046 moles, less than or equal to about 0.045 moles, less than or
equal to about 0.044 moles, less than or equal to about 0.043
moles, less than or equal to about 0.042 moles, less than or equal
to about 0.041 moles, or less than or equal to about 0.04 mol based
on one mole of the selenium. Without being bound by any particular
theory, the core may have various forms in terms of distributions
of Zn, Se, and Te.
In the core, Te may be dispersed in a ZnSe crystal structure. The
(average) size of the core may be greater than or equal to about 2
nm, greater than or equal to about 3 nm, or greater than or equal
to about 4 nm. The (average) size of the core may be less than or
equal to about 6 nm, for example less than or equal to about 5
nm.
The second semiconductor material may include a Group II-VI
compound, a Group III-V compound, a Group IV-VI compound, a Group
IV element or compound, a Group compound, a Group I--II-IV-VI
compound, or a combination thereof. The Group II-VI compound may be
a binary element compound such as CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO,
HgS, HgSe, HgTe, MgSe, MgS, or a mixture thereof; a ternary element
compound such as CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS,
HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS,
HgZnSe, HgZnTe, MgZnSe, MgZnS, or a mixture thereof; or a
quaternary element compound such as HgZnTeS, CdZnSeS, CdZnSeTe,
CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, or
a mixture thereof. The Group III-V compound may be a binary element
compound such as GaN, GaP, GaAs, GaSb, AlN, AIP, AIAs, AlSb, InN,
InP, InAs, InSb, or a mixture thereof; a ternary element compound
such as GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AINP, AINAs, AINSb,
AIPAs, AIPSb, InNP, InNAs, InNSb, InPAs, InPSb, or a mixture
thereof; or a quaternary element compound such as GaAINP, GaAINAs,
GaAlNSb, GaAIPAs, GaAIPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs,
GaInPSb, InAINP, InAINAs, InAINSb, InAIPAs, InAIPSb, or a mixture
thereof. The IV-VI compound may be a binary element compound such
as SnS, SnSe, SnTe, PbS, PbSe, PbTe, or a mixture thereof; a
ternary element compound such as SnSeS, SnSeTe, SnSTe, PbSeS,
PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe or a mixture thereof; or a
quaternary element compound such as SnPbSSe, SnPbSeTe, SnPbSTe, or
a mixture thereof. Examples of the Group I-III-VI compound may
include CuInSe.sub.2, CuInS.sub.2, CuInGaSe, and CuInGaS, but are
not limited thereto. Examples of the Group I-II-IV-VI compound may
include CuZnSnSe and CuZnSnS, but are not limited thereto. The
Group IV element or compound may be a single element such as Si,
Ge, or a mixture thereof; or a binary element compound such as SiC,
SiGe, or a mixture thereof. The Group III-V compound may further
include a Group II metal (e.g., InZnP etc.).
The shell may be a multi-layered shell including a plurality of
layers. Adjacent layers of the plurality of layers may include
semiconductor materials having different compositions from each
other. The shell may be a gradient alloy having a composition that
changes in a radial direction.
A thickness of the shell may be greater than or equal to about 0.5
nm, for example, greater than or equal to about 1 nm, greater than
or equal to about 2 nm, greater than or equal to about 3 nm,
greater than or equal to about 4 nm, or greater than or equal to
about 5 nm. A thickness of the shell may be less than or equal to
about 10 nm, less than or equal to about 9 nm, less than or equal
to about 8 nm, less than or equal to about 7 nm, less than or equal
to about 6 nm, less than or equal to about 5 nm, or less than or
equal to about 4 nm. The thickness of the shell may be determined
(calculated) from the sizes of the core and the semiconductor
nanocrystal particle.
In an embodiment, the second semiconductor material may include
zinc (Zn), selenium (Se), and sulfur (S). The shell may be a
multi-layered shell such as at least two-layered shell, at least
three-layered shell, at least four-layered shell, or the like. The
multi-layered shell may include a first layer disposed directly on
the core and outermost layer and the first layer may include ZnSeS
and the outermost layer may include ZnS. The shell may be a
gradient alloy and an amount of sulfur may have a concentration
gradient that increases as being apart from the core.
The semiconductor nanocrystal particle may have a ratio of a mole
amount of the tellurium relative to that of selenium (e.g.,
measured by inductively coupled plasma-atomic emission spectroscopy
(ICP-AES)) of less than or equal to about 0.05:1, less than or
equal to about 0.049:1, less than or equal to about 0.048:1, less
than or equal to about 0.047:1, less than or equal to about,
0.045:1, less than or equal to about 0.044:1, less than or equal to
about 0.043:1, less than or equal to about 0.042:1, less than or
equal to about 0.041:1, less than or equal to about 0.04:1, less
than or equal to about 0.039:1, less than or equal to about
0.035:1, less than or equal to about 0.03:1, less than or equal to
about 0.029:1, less than or equal to about 0.025:1, less than or
equal to about 0.024:1, less than or equal to about 0.023:1, less
than or equal to about 0.022:1, less than or equal to about
0.021:1, less than or equal to about 0.02:1, less than or equal to
about 0.019:1, less than or equal to about 0.018:1, less than or
equal to about 0.017:1, less than or equal to about 0.016:1, less
than or equal to about 0.015:1, less than or equal to about
0.014:1, less than or equal to about 0.013:1, less than or equal to
about 0.012:1, less than or equal to about 0.011:1, or less than or
equal to about 0.01:1. The mole ratio of the tellurium to the
selenium may be greater than or equal to about 0.001:1, greater
than or equal to about 0.002:1, greater than or equal to about
0.003:1, greater than or equal to about 0.004:1, greater than or
equal to about 0.005:1, greater than or equal to about 0.006:1, or
greater than or equal to about 0.007:1. The mole ratio of the
tellurium to the selenium may be about 0.004:1 to about 0.025:1.
The mole ratio of the tellurium to the selenium may be about 0.004
to about 0.023.
In the semiconductor nanocrystal particle, an amount of the zinc
may be greater than that of the selenium. In the semiconductor
nanocrystal particle, an amount of the zinc may be greater than
that of the tellurium.
An amount of zinc (Zn) may be greater than that of selenium (Se)
and an amount of selenium may be greater than that of tellurium,
for example when being confirmed by an ICP-AES analysis of the
semiconductor nanocrystal particle.
For example, in the ICP-AES analysis, a mole ratio of Se to Zn may
be less than about 1:1, for example, less than or equal to about
0.95:1, less than or equal to about 0.90:1, less than or equal to
about 0.85:1, or less than or equal to about 0.8:1.
For example, in an ICP-AES analysis, a mole ratio of Te to Zn may
be less than or equal to about 0.03:1, for example, less than or
equal to about 0.027:1, less than or equal to about 0.025:1, less
than or equal to about 0.02:1, less than or equal to about 0.019:1,
less than or equal to about 0.018:1, less than or equal to about
0.017:1, less than or equal to about 0.016:1, less than or equal to
about 0.015:1, less than or equal to about 0.014:1, less than or
equal to about 0.013:1, less than or equal to about 0.012:1, less
than or equal to about 0.011:1, less than or equal to about 0.01:1,
less than or equal to about 0.009:1, less than or equal to about
0.008:1, less than or equal to about 0.007:1, less than or equal to
about 0.006:1, or less than or equal to about 0.005:1. The mole
ratio of Te to Zn may be greater than or equal to about 0.001:1,
greater than or equal to about 0.002:1, or greater than or equal to
about 0.003:1. In a semiconductor nanocrystal particle according to
an embodiment, an amount of tellurium may be less than or equal to
about 1 wt % based on a total weight of the semiconductor
nanocrystal particle. The semiconductor nanocrystal particle may
not include cadmium.
In the semiconductor nanocrystal particle, a mole ratio of sulfur
to Zn may be greater than or equal to about 0.1:1, for example
greater than or equal to about 0.15:1, or greater than or equal to
about 0.2:1. In the semiconductor nanocrystal particle, the mole
ratio of sulfur to Zn may be less than or equal to about 0.5:1, for
example less than or equal to about 0.45:1. In the semiconductor
nanocrystal particle, a mole ratio of Se and S to zinc may be
greater than or equal to about 0.3:1, greater than or equal to
about 0.4:1, or greater than or equal to about 0.5:1. In the
semiconductor nanocrystal particle, a mole ratio of Se and S to
zinc may be less than or equal to about 1:1, for example less than
or equal to about 0.9:1.
The semiconductor nanocrystal may include various shapes. The
semiconductor nanocrystal may include a spherical shape, a
polygonal shape, a multipod shape, or a combination thereof. In an
embodiment, the semiconductor nanocrystal particle may have a
multipod shape. The multipod may have at least two (e.g., at least
three or at least four) branch parts and a valley part
therebetween.
A size of the semiconductor nanocrystal particle may be greater
than or equal to about 3 nm, for example greater than or equal to
about 4 nm, greater than or equal to about 5 nm, or greater than or
equal to about 6 nm. The size of the semiconductor nanocrystal may
be less than or equal to about 50 nm, for example less than or
equal to about 45 nm, less than or equal to about 40 nm, less than
or equal to about 35 nm, less than or equal to about 30 nm, less
than or equal to about 25 nm, less than or equal to about 24 nm,
less than or equal to about 23 nm, less than or equal to about 22
nm, less than or equal to about 21 nm, less than or equal to about
20 nm, less than or equal to about 19 nm, less than or equal to
about 18 nm, less than or equal to about 17 nm, or less than or
equal to about 16 nm. Herein, when the semiconductor nanocrystal
particle has a spherical shape, the size of the semiconductor
nanocrystal may be a diameter. When the particle has a polygonal or
multipod shape, the size of the particle may be the longest linear
length of, e.g., crossing or across, the particle. The size of the
semiconductor nanocrystal particle (or the core) may be determined
by for example, a Transmission Electron Microscope, but it is not
limited thereto.
A semiconductor nanocrystal particle according to an embodiment may
emit blue light having a maximum peak emission at a wavelength of
greater than or equal to about 430 nm (e.g., greater than or equal
to about 440 nm, greater than or equal to about 445 nm, or greater
than or equal to about 450 nm) and less than or equal to about 470
nm (e.g., less than about 470 nm, less than or equal to about 465
nm, or less than or equal to about 460 nm). The blue light may have
a maximum light-emitting peak wavelength of from about 450 nm to
about 460 nm. The maximum peak emission may have a full width at
half maximum (FWHM) of less than or equal to about 50 nm, for
example, less than or equal to about 49 nm, less than or equal to
about 48 nm, less than or equal to about 47 nm, less than or equal
to about 46 nm, less than or equal to about 45 nm, less than or
equal to about 44 nm, less than or equal to about 43 nm, less than
or equal to about 42 nm, less than or equal to about 41 nm, less
than or equal to about 40 nm, less than or equal to about 39 nm,
less than or equal to about 38 nm, less than or equal to about 37
nm, less than or equal to about 36 nm, less than or equal to about
35 nm, less than or equal to about 34 nm, less than or equal to
about 33 nm, less than or equal to about 32 nm, less than or equal
to about 31 nm, less than or equal to about 30 nm, less than or
equal to about 29 nm, or less than or equal to about 28 nm.
The semiconductor nanocrystal may have quantum efficiency of
greater than or equal to about 60%, for example, greater than or
equal to about 61%, greater than or equal to about 62%, greater
than or equal to about 63%, greater than or equal to about 64%,
greater than or equal to about 65%, greater than or equal to about
66%, greater than or equal to about 67%, greater than or equal to
about 68%, or greater than or equal to about 69%. The semiconductor
nanocrystal may have quantum efficiency of greater than or equal to
about 80%, greater than or equal to about 90%, greater than or
equal to about 95%, greater than or equal to about 99%, or about
100%.
A core-shell semiconductor nanocrystal including cadmium such as
CdSe/CdS may exhibit high photoluminescence properties and
stability against photooxidation by passivation of the surface of
the nanocrystal. Surfaces of these nanocrystals may be capped by an
inorganic shell having a wide bandgap. The inorganic shell
passivates the surface of the nanocrystal, effectively and/or
drastically, e.g., significantly, removes a dangling bond or a
coordination portion that form a trap for carriers formed inside
the nanocrystal, and thus photo-generated carriers may be confined
inside the core and relatively high luminous efficiency may be
realized. However, such a core-shell type semiconductor nanocrystal
generally has a maximum light emitting wavelength (i.e., a central
light emitting wavelength) of about 470 nm to about 630 nm and it
may be difficult to have, e.g., realize, a maximum light emitting
wavelength of less than about 470 nm. Because the maximum light
emitting wavelength of the semiconductor nanocrystal particles
increases with an increase of a size of the nanocrystal, a core
semiconductor nanocrystal having a very small size (e.g., less than
1.6 nm) may be necessary in order to obtain a maximum light
emitting wavelength of less than 470 nm, but it may be difficult to
produce a core having such a size with a narrow size distribution.
Formation of the shell on the core may cause an increase (e.g.,
red-shift) in a maximum light emitting peak wavelength of the
semiconductor nanocrystal. Therefore, it may be difficult to
prepare a core-shell semiconductor nanocrystal that emits blue
light.
The semiconductor nanocrystal according to an embodiment may
exhibit a maximum light emitting peak wavelength of less than about
470 nm, for example, less than or equal to about 465 nm with
relatively high quantum efficiency and a relatively narrow full
width at half maximum (FWHM) even if it has a relatively large core
size (e.g., about 2 nm or greater).
In an embodiment, a method of producing the semiconductor
nanocrystal particle includes
preparing a zinc precursor solution including a zinc precursor and
an organic ligand;
obtaining a selenium precursor and a tellurium precursor;
heating the zinc precursor solution at a first reaction temperature
and adding the selenium precursor and the tellurium precursor,
optionally an organic ligand to form a first semiconductor
nanocrystal core including zinc, selenium, and tellurium;
preparing a first shell precursor solution including a
metal-containing first shell precursor and an organic ligand;
obtaining a second shell precursor including a non-metal element;
and
heating the first shell precursor solution at a second reaction
temperature and adding the first semiconductor nanocrystal core and
the second shell precursor thereto to form a shell of a second
semiconductor nanocrystal on the first semiconductor nanocrystal
core. The method may further include separating the first
semiconductor nanocrystal core and dispersing it in an organic
solvent to prepare a core solution.
The zinc precursor may include a Zn powder, ZnO, an alkylated Zn
compound (e.g., C2 to C30 alkyl (e.g., dialkyl) zinc such as
dimethyl zinc, diethyl zinc), a Zn alkoxide (e.g., a zinc
ethoxide), a Zn carboxylate (e.g., a zinc acetate or zinc aliphatic
carboxylate, for example, zinc long chain aliphatic carboxylate
such as zinc oleate), a Zn nitrate, a Zn perchlorate, a Zn sulfate,
a Zn acetylacetonate, a Zn halide (e.g., a zinc chloride), a Zn
cyanide, a Zn hydroxide, or a combination thereof. The zinc
precursor solution may include at least two kinds of organic
ligands in an organic solvent. The at least two kinds of organic
ligands may include fatty acid and amine compounds. In a zinc
precursor solution, a concentration of the zinc precursor and a
concentration of the organic ligand are not particularly limited
and may be selected appropriately.
The selenium precursor may include selenium-trioctylphosphine
(Se-TOP), selenium-tributylphosphine (Se-TBP),
selenium-triphenylphosphine (Se-TPP), selenium-diphenylphosphine
(Se-DPP), or a combination thereof, but is not limited thereto. The
tellurium precursor may include tellurium-trioctylphosphine
(Te-TOP), tellurium-tributylphosphine (Te-TBP),
tellurium-triphenylphosphine (Te-TPP), or a combination thereof,
but is not limited thereto.
An amount of the selenium precursor for forming the core may be
greater than or equal to about 20 moles, for example, greater than
or equal to about 25 moles, greater than or equal to about 26
moles, greater than or equal to about 27 moles, greater than or
equal to about 28 moles, greater than or equal to about 29 moles,
greater than or equal to about 30 moles, greater than or equal to
about 31 moles, greater than or equal to about 32 moles, greater
than or equal to about 33 moles, greater than or equal to about 34
moles, greater than or equal to about 35 moles, greater than or
equal to about 36 moles, greater than or equal to about 37 moles,
greater than or equal to about 38 moles, greater than or equal to
about 39 moles, or greater than or equal to about 40 moles based on
one mole of the tellurium precursor. The amount of the selenium
precursor may be less than or equal to about 60 moles, less than or
equal to about 59 moles, less than or equal to about 58 moles, less
than or equal to about 57 moles, less than or equal to about 56
moles, or less than or equal to about 55 moles based on one mole of
the tellurium precursor. Within the foregoing ranges of the amount,
the core having the aforementioned composition may be formed.
The first reaction temperature may be greater than or equal to
about 280.degree. C., for example, greater than or equal to about
290.degree. C. A reaction time for forming the core is not
particularly limited and may be appropriately selected. For
example, the reaction time may be greater than or equal to about 5
minutes, greater than or equal to about 10 minutes, greater than or
equal to about 15 minutes, greater than or equal to about 20
minutes, greater than or equal to about 25 minutes, greater than or
equal to about 30 minutes, greater than or equal to about 35
minutes, greater than or equal to about 40 minutes, greater than or
equal to about 45 minutes, or greater than or equal to about 50
minutes, but is not limited thereto. For example, the reaction time
may be less than or equal to about 2 hours, less than or equal to
about 110 minutes, less than or equal to about 100 minutes, less
than or equal to about 90 minutes, less than or equal to about 80
minutes, less than or equal to about 70 minutes, or less than or
equal to about 60 minutes, but is not limited thereto. By
controlling the reaction time, the size of the core may be
controlled.
Hereinafter, shell precursors of the ZnSeS shell will be described
in detail, but the present disclosure is not limited thereto, and
desirable shell precursors may be selected in accordance with shell
compositions.
In an embodiment, the first shell precursor may include zinc. The
first shell precursor including zinc may be a zinc powder,
alkylated zinc (e.g., C2 to C30 alkyl (e.g., dialkyl) zinc, e.g.,
dimethyl zinc, diethyl zinc), a zinc alkoxide, a zinc carboxylate
(e.g., zinc aliphatic carboxylate, for example, zinc long chain
aliphatic carboxylate such as zinc oleate), a zinc nitrate, a zinc
perchlorate, a zinc sulfate, a zinc acetylacetonate, a zinc halide,
a zinc cyanide, a zinc hydroxide, ZnO, a zinc peroxide, or a
combination thereof, but is not limited thereto. Examples of the
first shell precursor may be dimethyl zinc, diethyl zinc, a zinc
acetate, a zinc acetylacetonate, a zinc iodide, a zinc bromide, a
zinc chloride, a zinc fluoride, a zinc carbonate, a zinc cyanide, a
zinc nitrate, a zinc oxide, a zinc peroxide, a zinc perchlorate, a
zinc sulfate, or a combination thereof.
The second shell precursor includes selenium, sulfur, or a
combination thereof. The sulfur-containing precursor of the second
shell precursor may be hexane thiol, octane thiol, decane thiol,
dodecane thiol, hexadecane thiol, mercapto propyl silane,
sulfur-trioctylphosphine (S-TOP), sulfur-tributylphosphine (S-TBP),
sulfur-triphenylphosphine (S-TPP), sulfur-trioctylamine (S-TOA),
bistrimethylsilyl sulfur, ammonium sulfide, sodium sulfide, or a
combination thereof.
The selenium-containing precursor of the second shell precursor may
be selenium-trioctylphosphine (Se-TOP), selenium-tributylphosphine
(Se-TBP), selenium-triphenylphosphine (Se-TPP),
selenium-diphenylphosphine (Se-DPP), or a combination thereof, but
is not limited thereto.
In an embodiment, after core synthesis and during a shell growth, a
solution including the shell precursors may be added to a reaction
system over several times (e.g., in stages) in order for a
composition of the shell to be changed or varied (e.g., in a radial
direction). As non-limiting examples, in a case in which a shell of
a ternary element (ABC) compound is formed, the sequence of the
addition of the precursors, the amount of the precursors, and the
reaction duration for the precursors (e.g., the A element precursor
(e.g., a metal element such as Zn), the B element precursor (e.g.,
a first non-metal element such as sulfur), the C element precursor
(e.g., a second non-metal element such as Se) solutions) may be
adjusted. For example, the core is added to the A element precursor
solution, the B element precursor solution is added thereto, and
then a reaction is performed for a predetermined time.
Subsequently, at least one of the C element precursor solution and
the B element precursor solution may be added to the reaction
system in a form of a mixture or individually and then a reaction
is performed. Herein, addition timing and the reaction time of the
C element precursor solution and the B element precursor solution
and a ratio of these precursors in the reaction system may be
controlled.
A lattice mismatch at an interface of the core and shell may be
controlled by controlling the addition times and the addition
timing of the C element precursor solution and the B element
precursor solution and a ratio of the precursors in the reaction
system. In addition, growth energy at the surface may be controlled
by changing a reaction temperature and, for example, a kind of, the
C element precursor.
The organic solvent may be a C6 to C22 primary amine such as a
hexadecylamine, a C6 to C22 secondary amine such as dioctylamine, a
C6 to C40 tertiary amine such as a trioctyl amine, a
nitrogen-containing heterocyclic compound such as pyridine, a C6 to
C40 olefin such as octadecene, a C6 to C40 aliphatic hydrocarbon
such as hexadecane, octadecane, or squalane, an aromatic
hydrocarbon substituted with a C6 to C30 alkyl group such as
phenyldodecane, phenyltetradecane, or phenyl hexadecane, a primary,
secondary, or tertiary phosphine (e.g., trioctyl phosphine)
substituted with at least one (e.g., 1, 2, or 3) C6 to C22 alkyl
group, a phosphine oxide (e.g., trioctylphosphine oxide)
substituted with at least one (e.g., 1, 2, or 3) C6 to C22 alkyl
group, a C12 to C22 aromatic ether such as a phenyl ether or a
benzyl ether, or a combination thereof.
The organic ligand may coordinate to, e.g., be bound to, the
surface of the produced nanocrystal and may have an effect on the
light emitting and electric characteristics as well as may
effectively disperse the nanocrystal in the solution phase. The
organic ligand may include RCOOH, RNH.sub.2, R.sub.2NH, R.sub.3N,
RSH, RH.sub.2PO, R.sub.2HPO, R.sub.3PO, RH.sub.2P, R.sub.2HP,
R.sub.3P, ROH, RCOOR, RHPOOH, RPO(OH).sub.2, RHPOOH (wherein, R is
the same or different and is independently include a C1 to C24
substituted or unsubstituted aliphatic hydrocarbon group, C6 to C20
substituted or unsubstituted aromatic hydrocarbon group, or a
combination thereof), or a combination thereof. The ligand may be
may be used alone or in a mixture of two or more compounds.
Examples of the organic ligand compound may include methane thiol,
ethane thiol, propane thiol, butane thiol, pentane thiol, hexane
thiol, octane thiol, dodecane thiol, hexadecane thiol, octadecane
thiol, benzyl thiol; methane amine, ethane amine, propane amine,
butane amine, pentane amine, hexane amine, octane amine, dodecane
amine, hexadecyl amine, oleyl amine, octadecyl amine, dimethyl
amine, diethyl amine, dipropyl amine; methanoic acid, ethanoic
acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid,
heptanoic acid, octanoic acid, dodecanoic acid, hexadecanoic acid,
octadecanoic acid, oleic acid, benzoic acid, palmitic acid, stearic
acid; phosphine such as methyl phosphine, ethyl phosphine, propyl
phosphine, butyl phosphine, pentyl phosphine, tributylphosphine, or
trioctylphosphine; a phosphine oxide compound such as methyl
phosphine oxide, ethyl phosphine oxide, propyl phosphine oxide,
butyl phosphine oxide, or trioctylphosphine oxide; a diphenyl
phosphine or triphenyl phosphine compound, or an oxide compound
thereof; phosphonic acid, or the like, but are not limited thereto.
The organic ligand compound may be used alone or in a mixture of
two or more compounds. In an embodiment, the organic ligand
compound may be a combination of RCOOH and amine (e.g., RNH.sub.2,
R.sub.2NH, and/or R.sub.3N).
Reaction conditions such as a reaction temperature or time for
shell formation is not particularly limited and may be selected
appropriately. In a non-limiting example embodiment, under a
vacuum, a solvent and optionally the ligand compound are heated (or
vacuum-treated) at a predetermined temperature (e.g., greater than
or equal to about 100.degree. C.), and are heated again at
predetermined temperature (e.g., greater than or equal to about
100.degree. C.) under an inert gas atmosphere. Subsequently, the
core is added, the shell precursors are sequentially or
simultaneously added, and then heated at a predetermined reaction
temperature to perform a reaction. Mixture having different ratios
of the shell precursors may be sequentially added for a reaction
time.
After the completion of the reaction, a non-solvent is added to
reaction products and the nanocrystal particles coordinated with,
e.g., bound to, the ligand compound may be separated. The
non-solvent may be a polar solvent that is miscible with the
solvent used in the core formation and/or shell formation reactions
and is not capable of dispersing the produced nanocrystals therein.
The non-solvent may be selected depending the solvent used in the
reaction and may be for example acetone, ethanol, butanol,
isopropanol, ethanediol, water, tetrahydrofuran (THF),
dimethylsulfoxide (DMSO), diethylether, formaldehyde, acetaldehyde,
a solvent having a similar solubility parameter to the foregoing
solvents, or a combination thereof. Separation of the nanocrystal
particles may involve centrifugation, sedimentation,
chromatography, or distillation. The separated nanocrystal
particles may be added to a washing solvent and washed, if desired.
Types of the washing solvent are not particularly limited and a
solvent having similar solubility parameter to that of the ligand
may be used and examples thereof may include hexane, heptane,
octane, chloroform, toluene, benzene, or the like.
In an embodiment, an electronic device includes the semiconductor
nanocrystal particle. The device may include a display device, a
light emitting diode (LED), an organic light emitting diode (OLED),
a quantum dot LED, a sensor, a solar cell, an image sensor, or a
liquid crystal display (LCD), but is not limited thereto.
In an embodiment, the electronic device may be a LCD device, a
photoluminescent element (e.g., a lighting such as a quantum dot
sheet or a quantum dot rail or a liquid crystal display (LCD)) or a
backlight unit for an electroluminescent device (e.g., QD LED).
In a non-limiting embodiment, the electronic device may include a
quantum dot sheet and the semiconductor nanocrystal particle may be
included in the quantum dot sheet (e.g., in a form of a
semiconductor nanocrystal-polymer composite).
In a non-limiting embodiment, the electronic device may be an
electroluminescent device. The electronic device may include an
anode 1 and a cathode 5 facing each other and a quantum dot
emission layer 3 disposed between the anode and the cathode and
including a plurality of quantum dots, and the plurality of quantum
dots may include the blue light emitting semiconductor nanocrystal
particle (see FIG. 2).
The cathode may include an electron injection conductor (for
example, having a relatively low work function). The anode may
include a hole injection conductor (for example, having a
relatively high work function). The electron/hole injection
conductors may include a metal (e.g., aluminum, magnesium,
tungsten, nickel, cobalt, platinum, palladium, calcium, or LiF), a
metal compound, an alloy, or a combination thereof; a metal oxide
such as gallium indium oxide or indium tin oxide; or a conductive
polymer such as polyethylene dioxythiophene (e.g., having a
relatively high work function), but are not limited thereto.
At least one of the cathode and the anode may be a light
transmitting electrode or a transparent electrode. In an
embodiment, both of the anode and the cathode may be light
transmitting electrodes. The electrode may be patterned.
The light transmitting electrode may be made of, for example a
transparent conductor such as indium tin oxide (ITO) or indium zinc
oxide (IZO), gallium indium tin oxide, zinc indium tin oxide,
titanium nitride, polyaniline, or LiF/Mg:Ag, or a metal thin film
of a thin monolayer or multilayer, but is not limited thereto. When
one of the cathode and the anode is a non-light transmitting
electrode, it may be made of, for example, an opaque conductor such
as aluminum (Al), a lithium aluminum (Li:Al) alloy, a
magnesium-silver alloy (Mg:Ag), or a lithium fluoride-aluminum
(LiF:Al).
The light transmitting electrode may be disposed on a transparent
substrate (e.g., insulating transparent substrate). The substrate
may be rigid or flexible. The substrate may be a plastic, glass, or
a metal.
Thicknesses of the anode and the cathode are not particularly
limited and may be selected considering device efficiency. For
example, the thickness of the anode (or the cathode) may be greater
than or equal to about 5 nm, for example, greater than or equal to
about 50 nm, but is not limited thereto. For example, the thickness
of the anode (or the cathode) may be less than or equal to about
100 micrometers (.mu.m), for example, less than or equal to about
10 um, less than or equal to about 1 .mu.m, less than or equal to
about 900 nm, less than or equal to about 500 nm, or less than or
equal to about 100 nm, but is not limited thereto.
The quantum dot emission layer includes a plurality of quantum
dots. The plurality of quantum dots includes the blue light
emitting semiconductor nanocrystal particle according to the
aforementioned embodiments. The quantum dot emission layer may
include a monolayer of the blue light emitting semiconductor
nanocrystal particles.
The quantum dot emission layer may be formed by preparing a
dispersion including the quantum dots dispersed in a solvent,
applying the dispersion via spin coating, ink jet coating, or spray
coating, and drying the same. The emissive layer may have a
thickness of greater than or equal to about 5 nm, for example,
greater than or equal to about 10 nm, greater than or equal to
about 15 nm, greater than or equal to about 20 nm, or greater than
or equal to about 25 nm, and less than or equal to about 100 nm,
for example, less than or equal to about 90 nm, less than or equal
to about 80 nm, less than or equal to about 70 nm, less than or
equal to about 60 nm, less than or equal to about 50 nm, less than
or equal to about 40 nm, or less than or equal to about 30 nm.
The electronic device may include charge (hole or electron)
auxiliary layers between the anode and the cathode. For example,
the electronic device may include a hole auxiliary layer 2 or an
electron auxiliary layer 4 between the anode and the quantum dot
emission layer and/or between the cathode and the quantum dot
emission layer. (see FIG. 2)
In the figures, the electron/hole auxiliary layer is formed as a
single layer, but it is not limited thereto and may include a
plurality of layers including at least two stacked layers.
The hole auxiliary layer may include for example a hole injection
layer (HIL) to facilitate hole injection, a hole transport layer
(HTL) to facilitate hole transport, an electron blocking layer
(EBL) to inhibit electron transport, or a combination thereof. For
example, the hole injection layer may be disposed between the hole
transport layer and the anode. For example, the electron blocking
layer may be disposed between the emission layer and the hole
transport (injection) layer, but is not limited thereto. A
thickness of each layer may be selected appropriately. For example,
a thickness of each layer may be greater than or equal to about 1
nm, greater than or equal to about 5 nm, greater than or equal to
about 10 nm, greater than or equal to about 15 nm, greater than or
equal to about 20 nm, or greater than or equal to about 25 nm, and
less than or equal to about 500 nm, less than or equal to about 400
nm, less than or equal to about 300 nm, less than or equal to about
200 nm, less than or equal to about 100 nm, less than or equal to
about 90 nm, less than or equal to about 80 nm, less than or equal
to about 70 nm, less than or equal to about 60 nm, or less than or
equal to about 50 nm, but is not limited thereto. The hole
injection layer may be an organic layer that is formed by a
solution process (e.g., spin coating etc.) such as PEDOT:PSS. The
hole transport layer may be an organic layer that is formed by a
solution process (e.g., spin coating etc.).
The electron auxiliary layer may include for example an electron
injection layer (EIL) to facilitate electron injection, an electron
transport layer (ETL) to facilitate electron transport, a hole
blocking layer (HBL) to inhibit hole transport, or a combination
thereof. For example, the electron injection layer may be disposed
between the electron transport layer and the cathode. For example,
the hole blocking layer may be disposed between the emission layer
and the electron transport (injection) layer, but is not limited
thereto. A thickness of each layer may be selected appropriately.
For example, a thickness of each layer may be greater than or equal
to about 1 nm, greater than or equal to about 5 nm, greater than or
equal to about 10 nm, greater than or equal to about 15 nm, greater
than or equal to about 20 nm, or greater than or equal to about 25
nm, and less than or equal to about 500 nm, less than or equal to
about 400 nm, less than or equal to about 300 nm, less than or
equal to about 200 nm, less than or equal to about 100 nm, less
than or equal to about 90 nm, less than or equal to about 80 nm,
less than or equal to about 70 nm, less than or equal to about 60
nm, less than or equal to about 50 nm, but is not limited thereto.
The electron injection layer may be an organic layer formed by
deposition. The electron transport layer may include an inorganic
oxide or a (nano or fine) particles thereof or may include an
organic layer formed by deposition.
The quantum dot emission layer may be disposed in or on the hole
injection (or transport) layer or an electron injection (or
transport) layer. The quantum dot emission layer may be disposed as
a separate layer between the hole auxiliary layer and the electron
auxiliary layer.
The charge auxiliary layer, the electron blocking layer, and the
hole blocking layer may include for example an organic material, an
inorganic material, or an organic/inorganic material. The organic
material may be a compound having hole or electron-related
properties. The inorganic material may be for example a metal oxide
such as molybdenum oxide, tungsten oxide, zinc oxide, or nickel
oxide, but is not limited thereto.
The hole transport layer (HTL) and/or the hole injection layer may
include for example poly(3,4-ethylenedioxythiophene):poly(styrene
sulfonate) (PEDOT:PSS),
poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine)
(TFB), polyarylamine, poly(N-vinylcarbazole, PVK), polyaniline,
polypyrrole, N,N,N',N'-tetrakis (4-methoxyphenyl)-benzidine (TPD),
4,4',-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (.alpha.-NPD),
m-MTDATA (4,4',4''-tris[phenyl(m-tolyl)amino]triphenylamine),
4,4',4''-tris(N-carbazolyl)-triphenylamine (TCTA),
1,1-bis[(di-4-tolylamino)phenylcyclohexane (TAPC), a p-type metal
oxide (e.g., NiO, WO.sub.3, MoO.sub.3, etc.), a carbonaceous
material such as grapheme oxide, or a combination thereof, but is
not limited thereto.
The electron blocking layer (EBL) may include for example
poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)
(PEDOT:PSS),
poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB)
polyarylamine, poly(N-vinylcarbazole), polyaniline, polypyrrole,
N,N,N',N'-tetrakis(4-methoxyphenyl)-benzidine (TPD),
4-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (.alpha.-NPD),
m-MTDATA, 4,4',4''-tris(N-carbazolyl)-triphenylamine (TCTA), or a
combination thereof, but is not limited thereto.
The electron transport layer (ETL) and/or the electron injection
layer may include for example 1,4,5,8-naphthalene-tetracarboxylic
dianhydride (NTCDA), bathocuproine (BCP),
tris[3-(3-pyridyl)-mesityl]borane (3TPYMB), LiF, Alq.sub.3,
Gaq.sub.3, Inq.sub.3, Znq.sub.2, Zn(BTZ).sub.2, BeBq.sub.2, ET204
(8-(4-(4,6-di(naphthalen-2-yl)-1,3,5-triazin-2-yl)phenyl)quinolone),
8-hydroxyquinolinato lithium (Liq), an n-type metal oxide (e.g.,
ZnO, HfO.sub.2, etc.), or a combination thereof, but is not limited
thereto. In the foregoing "q" is 8-hydroxyquinoline, "BTZ" is
2-(2-hydroxyphenyl)benzothiazolate, and "Bq" is
10-hydroxybenzo[h]quinoline.
The hole blocking layer (HBL) may include for example
1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA),
bathocuproine (BCP), tris[3-(3-pyridyl)-mesityl] borane (3TPYMB),
LiF, Alq.sub.3, Gaq.sub.3, Inq.sub.3, Znq.sub.2, Zn(BTZ).sub.2,
BeBq.sub.2, or a combination thereof, but is not limited
thereto.
In a device according to an embodiment, an anode 10 disposed on a
transparent substrate 100 may include a metal oxide transparent
electrode (e.g., ITO electrode) and a cathode 50 facing the anode
may include a metal (Mg, Al, etc.) of a predetermined (e.g.,
relatively low) work function. For example, a hole auxiliary layer
20 (e.g., a hole transport layer including TFB and/or PVK and/or a
hole injection layer including PEDOT:PSS and/or a p-type metal
oxide) may be disposed between the transparent electrode 10 and the
emission layer 30. An electron auxiliary layer (e.g., electron
transport layer) 40 may be disposed between the quantum dot
emission layer 30 and the cathode 50. (see FIG. 3)
A device according to an embodiment has an inverted structure.
Herein, a cathode 50 disposed on a transparent substrate 100 may
include a metal oxide transparent electrode (e.g., ITO) and an
anode 10 facing the cathode may include a metal (e.g., Au, Ag,
etc.) of a predetermined (e.g., relatively high) work function. For
example, an n-type metal oxide (ZnO) may be disposed between the
transparent electrode 50 and the emission layer 30 as an electron
auxiliary layer (e.g., an electron transport layer) 40. A hole
auxiliary layer 20 (e.g., a hole transport layer including TFB
and/or PVK and/or a hole injection layer including MoO.sub.3 or
another p-type metal oxide) may be disposed between the metal anode
10 and the quantum dot emission layer 30. (see FIG. 4)
Hereinafter, specific examples are illustrated. However, these
examples are exemplary, and the present disclosure is not limited
thereto.
EXAMPLES
Analysis Method
[1] Photoluminescence Analysis
A photoluminescence (PL) spectrum of the produced nanocrystals are
obtained using a Hitachi F-7000 spectrometer at an irradiation
wavelength of 372 nm.
[2] Ultraviolet (UV) Spectroscopy Analysis
UV spectroscopy analysis is performed using a Hitachi U-3310
spectrometer to obtain a UV-Visible absorption spectrum.
[3] TEM Analysis
(1) Transmission electron microscope photographs of nanocrystals
are obtained using an UT F30 Tecnai electron microscope.
(2) TEM-EDX analysis (elemental mapping) is performed using an UT
F30 Tecnai electron microscope.
[4] ICP Analysis
An inductively coupled plasma-atomic emission spectroscopy
(ICP-AES) analysis is performed using Shimadzu ICPS-8100.
[5] HRTEM Analysis
A HRTEM analysis is performed using TEM-Titan G2.
[6] X-Ray Diffraction Analysis
XRD analysis is performed using a Philips XPert PRO equipment with
a power of 3 kW to confirm crystal structures of the semiconductor
nanocrystals.
Synthesis is performed under an inert gas atmosphere (nitrogen
flowing condition) unless particularly mentioned.
Example 1: Production of ZnTeSe Core I
Selenium and tellurium are dispersed in trioctylphosphine (TOP) to
obtain a 2 M Se/TOP stock solution and a 0.1 M Te/TOP stock
solution.
10 milliliters (mL) of trioctylamine is added to a reactor together
with 0.125 millimoles (mmol) of zinc acetate, 0.25 mmol of palmitic
acid, and 0.25 mmol of hexadecyl amine and the mixture is heated
under a vacuum at 120.degree. C. In one hour, an atmosphere in the
reactor is converted into nitrogen.
After the mixture is heated at 300.degree. C., the prepared Se/TOP
stock solution and Te/TOP stock solution are rapidly added in a
Te/Se ratio of 1/25. After 10 minutes (10 m), 30 minutes (30 m), or
60 minutes (60 m), acetone is added to a reaction solution that is
rapidly cooled to room temperature and precipitates obtained by
centrifugation are dispersed in toluene. UV-vis spectroscopy
analysis and photoluminescence spectroscopy analysis of the
obtained semiconductor nanocrystal particle are performed and the
results are shown in FIGS. 5 and 6. As a result, it is confirmed
that the obtained semiconductor nanocrystal has a first absorption
maximum wavelength of 400 nm to 430 nm and a maximum peak emission
wavelength of 430 nm to 460 nm. It is confirmed that quantum
efficiency of the produced semiconductor nanocrystal is about
30-40%.
A transmission electron microscope image of the semiconductor
nanocrystal particle where a reaction time is 60 minutes is shown
in FIG. 7. A HRTEM image of the semiconductor nanocrystal particle
where a reaction time is 60 minutes is shown in FIG. 8. From the
transmission electron microscope analysis result, it is confirmed
that spherical shapes/polygon particles are formed. An X-ray
diffraction analysis of the semiconductor nanocrystal particle
where a reaction time is 60 minutes is performed and the result is
shown in FIG. 9. From the result of FIG. 9, it is confirmed that
the produced core has a ZnSe cubic crystal structure.
Examples 2-1 to 2-5: Production of ZnTeSe Core II
The cores are prepared in the same manner as set forth in Example 1
except that the ratios of selenium and tellurium are changed as set
forth in Table 1 (reaction time: 30 to 60 minutes).
Maximum light emitting peak wavelengths and full widths at half
maximum (FWHM) of the prepared cores and the weight ratios of
tellurium of the produced semiconductor nanocrystal (confirmed by
ICP) are compiled in Table 1.
TABLE-US-00001 TABLE 1 Maximum light Full width Te/Se ratio
emitting peak at half Amount of Reaction wavelength maximum of Te
system (nm) (FWHM) (nm) (wt %) Example 2-1 0 422 24 0 Example 2-2
1/50 431 48 1.78 Example 2-3 1/30 441 57 2.82 Example 2-4 1/25 445
57 3.34 Example 2-5 1/8 478 67 7.5
Example 3: Core-Shell Semiconductor Nanocrystal of ZnTeSe
Core/Shell of ZnSeS Gradient Composition
1.8 mmol (0.336 grams (g)) of zinc acetate, 3.6 mmol (1.134 g) of
oleic acid, and 10 mL of trioctylamine are added to a flask and
vacuum-treated at 120.degree. C. for 10 minutes. The inside
atmosphere of the flask is substituted with nitrogen (N.sub.2) and
then a temperature is increased to 180.degree. C. The ZnTeSe core
(reaction time: 60 minutes) prepared in Example 1 is added thereto
within 10 seconds, subsequently 0.04 mmol of Se/TOP is slowly
added, and a temperature is increased to 280.degree. C. Then, 0.01
mmol of S/TOP is added and a temperature is increased to
320.degree. C. and a reaction is performed for 10 minutes.
Subsequently, a mixed solution including 0.02 mmol of Se/TOP and
0.04 mmol of S/TOP is slowly added, and a reaction is performed for
20 minutes (hereinafter, this step may be referred to as step A).
Then, mixing ratios of Se and S are changed, and then the mixed
solutions of Se and S are added, and reactions are performed for 20
minutes. Herein, the mixed solution of Se and S are a mixed
solution of Se/TOP 0.01 mmol+S/TOP 0.05 mmol, a mixed solution
(hereinafter, this step may be referred to as step B) of Se/TOP
0.005 mmol+S/TOP 0.1 mmol, and a solution of S/TOP 0.5 mmol, which
are sequentially used.
The reactions are completed, the reactor is cooled, and the
obtained nanocrystal particles are centrifuged with ethanol and
dispersed in toluene.
UV-vis spectroscopy analysis, photoluminescence analysis, and
transmission electron microscope analysis of the nanocrystals
during the production (core, step A, and step B) and (core-shell)
nanocrystals as prepared are performed and the results are shown in
FIGS. 10, 11, and 12.
From the photoluminescence analysis result, it is confirmed that
the produced quantum dot has a maximum light emitting peak of 449
nm (full width at half maximum (FWHM) 28 nm) and quantum efficiency
of 70%.
The results confirmed that the formation of the shell causes a
shift of the maximum luminescent peak wavelength to a longer
wavelength and a decrease in the FWHM and an increase in the
quantum yield.
It is confirmed that the semiconductor nanocrystal particle as
prepared has a multipod shape.
It is confirmed that the semiconductor nanocrystal particle as
prepared have a particle diameter of 10 nm to 20 nm.
An inductively coupled plasma atom light emitting spectroscopy
analysis of ZnTeSe core and ZnTeSe (core)/ZnSeS/ZnS is performed
and the results (a mole ratio to Zn) are shown in Table 2.
TABLE-US-00002 TABLE 2 S Zn Se Te (Se + S)/Zn ZnTeSe core 0 1 0.792
0.018 0.792 ZnTeSe 0.390 1 0.472 0.004 0.862 (core)/ZnSeS/ZnS
A TEM-EDX analysis (elemental mapping) of the produced
semiconductor nanocrystal particle is performed and the result is
shown in FIG. 13. From FIG. 13, it is confirmed that a shell having
an outer-layer including the sulfur is formed.
Comparative Example 1
ZnTeSe (core)/ZnSeS/ZnS (shell) particles are prepared in the same
manner as set forth in Example 3 except for using a core prepared
in Example 2-5 (the ratio between the precursors Te/Se=1/8). An
ICP-AES analysis is performed for the prepared ZnTeSe
(core)/ZnSeS/ZnS (shell) particles. The results confirm that the
mole ratio of the tellurium to the selenium is 0.024. The
photoluminescent analysis is made for the prepared particles. The
results confirm that the PL wavelength thereof is 487 nm, the FWHM
is 44 nm, and the QY is 37%.
While this disclosure has been described in connection with what is
presently considered to be practical example embodiments, it is to
be understood that the invention is not limited to the disclosed
embodiments, but, on the contrary, is intended to cover various
modifications and equivalent arrangements included within the
spirit and scope of the appended claims.
* * * * *